Transcript Lecture Slides

Chapter 3
The Molecules of Life
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
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Biology and Society:
Got Lactose?
• Lactose is the main sugar found in milk.
• Some adults exhibit lactose intolerance, the inability to properly
digest lactose.
• Lactose-intolerant individuals are unable to digest lactose
properly.
– Lactose is broken down by bacteria in the large intestine producing
gas and discomfort.
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Figure 3.00
• There is no treatment for the underlying cause of lactose
intolerance.
• Affected people must
– Avoid lactose-containing foods or
– Take the enzyme lactase when eating dairy products
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ORGANIC COMPOUNDS
• A cell is mostly water.
• The rest of the cell consists mainly of carbon-based molecules.
• Carbon forms large, complex, and diverse molecules necessary
for life’s functions.
• Organic compounds are carbon-based molecules.
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Carbon Chemistry
• Carbon is a versatile atom.
– It has four electrons in an outer shell that holds eight.
– Carbon can share its electrons with other atoms to form up to four
covalent bonds.
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• Carbon can use its bonds to
– Attach to other carbons
– Form an endless diversity of carbon skeletons
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Carbon skeletons vary in length
Double bond
Carbon skeletons may have double bonds,
which can vary in location
Carbon skeletons may be unbranched or branched
Carbon skeletons may be arranged in rings
Figure 3.1
Carbon skeletons vary in length
Figure 3.1a
Double bond
Carbon skeletons may have double bonds,
which can vary in location
Figure 3.1b
Carbon skeletons may be unbranched or branched
Figure 3.1c
Carbon skeletons may be arranged in rings
Figure 3.1d
• The simplest organic compounds are hydrocarbons, which are
organic molecules containing only carbon and hydrogen atoms.
• The simplest hydrocarbon is methane, consisting of a single
carbon atom bonded to four hydrogen atoms.
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Structural formula
Ball-and-stick model
Space-filling model
Figure 3.2
• Larger hydrocarbons form fuels for engines.
• Hydrocarbons of fat molecules fuel our bodies.
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Figure 3.3
• Each type of organic molecule has a unique three-dimensional
shape.
• The shapes of organic molecules relate to their functions.
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• The unique properties of an organic compound depend on
– Its carbon skeleton
– The atoms attached to the skeleton
• The groups of atoms that usually participate in chemical reactions
are called functional groups. Two common examples are
– Hydroxyl groups (-OH)
– Carboxyl groups (C=O)
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Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are gigantic,
earning the name macromolecules.
• Three categories of macromolecules are
– Carbohydrates
– Proteins
– Nucleic acids
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• Most macromolecules are polymers.
• Polymers are made by stringing together many smaller molecules
called monomers.
• A dehydration reaction
– Links two monomers together
– Removes a molecule of water
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Short polymer
Monomer
Dehydration
reaction
Hydrolysis
Longer polymer
a Building a polymer chain
b Breaking a polymer chain
Figure 3.4
Short polymer
Monomer
Dehydration
reaction
Longer polymer
a Building a polymer chain
Figure 3.4a
Hydrolysis
b Breaking a polymer chain
Figure 3.4b
• Organisms also have to break down macromolecules.
• Hydrolysis
– Breaks bonds between monomers
– Adds a molecule of water
– Reverses the dehydration reaction
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LARGE BIOLOGICAL MOLECULES
• There are four categories of large molecules in cells:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Carbohydrates
• Carbohydrates are sugars or sugar polymers. They include
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
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Monosaccharides
• Monosaccharides are simple sugars that cannot be broken down
by hydrolysis into smaller sugars.
• Common examples are
– Glucose in sports drinks
– Fructose found in fruit
• Glucose and fructose are isomers, molecules that have the same
molecular formula but different structures.
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Glucose
Fructose
C6H12O6
C6H12O6
Isomers
Figure 3.5a
• Monosaccharides are the main fuels for cellular work.
• In aqueous solutions, many monosaccharides form rings.
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b Abbreviated
ring structure
a Linear and ring structures
Figure 3.6
Disaccharides
• A disaccharide is
– A double sugar
– Constructed from two monosaccharides
– Formed by a dehydration reaction
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Galactose
Glucose
Lactose
Figure 3.7
• Disaccharides include
– Lactose in milk
– Maltose in beer, malted milk shakes, and malted milk ball candy
– Sucrose in table sugar
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• Sucrose is
– The main carbohydrate in plant sap
– Rarely used as a sweetener in processed foods
• High-fructose corn syrup is made by a commercial process that
converts natural glucose in corn syrup to much sweeter fructose.
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processed to extract
Starch
broken down into
Glucose
converted to sweeter
Fructose
added to foods as
high-fructose corn syrup
Ingredients: carbonated water,
high-fructose corn syrup,
caramel color, phosphoric acid,
natural flavors
Figure 3.8
• The United States is one of the world’s leading markets for
sweeteners.
– The average American consumes about 45 kg of sugar (about 100
lbs.) per year.
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Polysaccharides
• Polysaccharides are
– Complex carbohydrates
– Made of long chains of sugar units and polymers of
monosaccharides
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Glucose
monomer
Starch granules
a Starch
Glycogen
granules
b Glycogen
Cellulose fibril
Cellulose
molecules
c Cellulose
Figure 3.9
• Starch is
– A familiar example of a polysaccharide
– Used by plant cells to store energy
• Potatoes and grains are major sources of starch in the human diet.
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• Glycogen is
– Used by animals cells to store energy
– Converted to glucose when it is needed
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• Cellulose
– Is the most abundant organic compound on Earth
– Forms cable-like fibrils in the tough walls that enclose plants
– Cannot be broken apart by most animals
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• Monosaccharides and disaccharides dissolve readily in water.
• Cellulose does not dissolve readily in water.
• Almost all carbohydrates are hydrophilic, or “water-loving,”
adhering water to their surface.
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Lipids
• Lipids are
–
Neither macromolecules nor polymers
–
Hydrophobic, unable to mix with water
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Oil (hydrophobic)
Vinegar (hydrophilic)
Figure 3.10
Fats
• A typical fat, or triglyceride, consists of a glycerol molecule
joined with three fatty acid molecules via a dehydration reaction.
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Fatty acid
Glycerol
(a) A dehydration reaction linking a fatty acid to glycerol
(b) A fat molecule with a glycerol “head” and three
energy-rich hydrocarbon fatty acid “tails”
Figure 3.11
• Fats perform essential functions in the human body including
– Energy storage
– Cushioning
– Insulation
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• If the carbon skeleton of a fatty acid has
– Fewer than the maximum number of hydrogens, it is unsaturated
– The maximum number of hydrogens, then it is saturated
• A saturated fat has no double bonds, and all three of its fatty acids
are saturated.
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• Most animal fats
– Have a high proportion of saturated fatty acids
– Can easily stack, tending to be solid at room temperature
– Contribute to atherosclerosis, a condition in which lipidcontaining plaques build up within the walls of blood vessels
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• Most plant oils tend to be low in saturated fatty acids and liquid at
room temperature.
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• Hydrogenation
– Adds hydrogen
– Converts unsaturated fats to saturated fats
– Makes liquid fats solid at room temperature
– Creates trans fat, a type of unsaturated fat that is even less healthy
than saturated fats
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TYPES OF FATS
Saturated Fats
Unsaturated Fats
Margarine
INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED
COTTONSEED OIL, PARTIALLY HYDROGENATED
COTTONSEED OIL AND SOYBEAN OILS, MONO AND
DIGLYCERIDES, TBHO AND CITRIC ACID
Plant oils
Trans fats
ANTIOXIDANTS
Omega-3 fats
Figure 3.12
Steroids
• Steroids are very different from fats in structure and function.
– The carbon skeleton is bent to form four fused rings.
– Steroids vary in the functional groups attached to this core set of
rings.
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• Cholesterol is
– A key component of cell membranes
– The “base steroid” from which your body produces other steroids,
such as estrogen and testosterone
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Cholesterol
Testosterone
A type of estrogen
Figure 3.13
• Synthetic anabolic steroids
– Resemble testosterone
– Mimic some of its effects
– Can cause serious physical and mental problems
– Are abused by athletes to enhance performance
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THG
Figure 3.14
Proteins
• Proteins
– Are polymers constructed from amino acid monomers
– Perform most of the tasks the body needs to function
– Form enzymes, chemicals that change the rate of a chemical
reaction without being changed in the process
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MAJOR TYPES OF PROTEINS
Structural Proteins
Storage Proteins
Contractile Proteins
Transport Proteins
Enzymes
Figure 3.15
The Monomers of Proteins: Amino Acids
• All proteins are constructed from a common set of 20 kinds of
amino acids.
• Each amino acid consists of a central carbon atom bonded to four
covalent partners in which three of those attachment groups are
common to all amino acids.
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Amino
group
Carboxyl
group
Side
group
a The general structure of an amino acid
Hydrophobic
side group
Hydrophilic
side group
Leucine
Serine
b Examples of amino acids with hydrophobic and hydrophilic
side groups
Figure 3.16
Proteins as Polymers
• Cells link amino acids together by dehydration reactions, forming
peptide bonds and creating long chains of amino acids called
polypeptides.
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Carboxyl
group
Amino
group
Side
group
Side
group
Amino acid
Amino acid
Dehydration reaction
Side
group
Side
group
Peptide bond
Figure 3.17-2
• Your body has tens of thousands of different kinds of protein.
• Proteins differ in their arrangement of amino acids.
• The specific sequence of amino acids in a protein is its primary
structure.
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15
5
1
10
30
35
20
25
45
40
50
55
65
60
70
75
Amino acid
85
80
95
100
90
110
115
105
125
120
129
Figure 3.18
• A slight change in the primary structure of a protein affects its
ability to function.
• The substitution of one amino acid for another in hemoglobin
causes sickle-cell disease.
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SEM
1
2
Normal red blood cell
3
4
5
6
7. . . 146
Normal hemoglobin
SEM
a Normal hemoglobin
1
Sickled red blood cell
2
3
4
5
6
7. . . 146
Sickle-cell hemoglobin
b Sickle-cell hemoglobin
Figure 3.19
Protein Shape
• A functional protein consists of one or more polypeptide chains,
precisely folded and coiled into a molecule of unique shape.
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• Proteins consisting of
– One polypeptide have three levels of structure
– More than one polypeptide chain have a fourth, quaternary
structure
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Amino
acids
b Secondary structure
c Tertiary
structure
d Quaternary
structure
a Primary
structure
Pleated sheet
Protein with
four polypeptides
Polypeptide
Alpha helix
Figure 3.20-4
• A protein’s three-dimensional shape
– Recognizes and binds to another molecule
– Enables the protein to carry out its specific function in a cell
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Target
Protein
Figure 3.21
What Determines Protein Shape?
• A protein’s shape is sensitive to the surrounding environment.
• Unfavorable temperature and pH changes can cause
denaturation of a protein, in which it unravels and loses its
shape.
• High fevers (above 104º F) in humans can cause some proteins to
denature.
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• Misfolded proteins are associated with
– Alzheimer’s disease
– Mad cow disease
– Parkinson’s disease
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Nucleic Acids
• Nucleic acids
– Are macromolecules that provide the directions for building
proteins
– Include DNA and RNA
– Are the genetic material that organisms inherit from their parents
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• DNA resides in cells in long fibers called chromosomes.
• A gene is a specific stretch of DNA that programs the amino acid
sequence of a polypeptide.
• The chemical code of DNA must be translated from “nucleic acid
language” to “protein language.”
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Gene
DNA
Nucleic acids
RNA
Amino acid
Protein
Figure 3.22
•
Nucleic acids are polymers of nucleotides.
•
Each nucleotide has three parts:
–
A five-carbon sugar
–
A phosphate group
–
A nitrogenous base
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Nitrogenous base
A, G, C, or T
Thymine T
Phosphate
group
Phosphate
Base
Sugar
deoxyribose
a Atomic structure
Sugar
b Symbol used in this book
Figure 3.23
• Each DNA nucleotide has one of the following bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
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Adenine A
Thymine T
Guanine G
Cytosine C
Figure 3.24a
Adenine A
Guanine G
Thymine T Cytosine C
Space-filling model of DNA
Figure 3.24b
• Dehydration reactions
– Link nucleotide monomers into long chains called polynucleotides
– Form covalent bonds between the sugar of one nucleotide and the
phosphate of the next
– Form a sugar-phosphate backbone
• Nitrogenous bases hang off the sugar-phosphate backbone.
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Sugar-phosphate
backbone
Base
Nucleotide
pair
Hydrogen
bond
Bases
a DNA strand
polynucleotide
b Double helix
two polynucleotide strands
Figure 3.25
• Two strands of DNA join together to form a double helix.
• Bases along one DNA strand hydrogen-bond to bases along the
other strand.
• The functional groups hanging off the base determine which bases
pair up:
– A only pairs with T.
– G can only pair with C.
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• RNA, ribonucleic acid, is different from DNA.
– RNA is usually single-stranded but DNA usually exists as a double
helix.
– RNA uses the sugar ribose and the base uracil (U) instead of
thymine (T).
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Nitrogenous base
A, G, C, or U
Uracil U
Phosphate
group
Sugar ribose
Figure 3.26
The Process of Science:
Does Lactose Intolerance Have a Genetic Basis?
• Observation: Most lactose-intolerant people have a normal
version of the lactase gene.
• Question: Is there a genetic basis for lactose intolerance?
• Hypothesis: Lactose-intolerant people have a mutation but not
within the lactase gene.
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• Prediction: A mutation would be found nearby the lactase gene.
• Experiment: Genes of 196 lactose-intolerant people were
examined.
• Results: A 100% correlation between lactose intolerance and one
mutation was found.
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DNA
Lactase gene
14,000 nucleotides
Human cell
Chromosome 2
Section of
DNA in 46
one DNA molecule chromosome 2
chromosomes
C at this site causes
lactose intolerance
T at this site causes
lactose tolerance
Figure 3.27
Evolution Connection:
Evolution and Lactose Intolerance in Humans
• Most people are lactose-intolerant as adults:
– African Americans and Native Americans — 80%
– Asian Americans — 90%
– But only 10% of Americans of northern European descent are
lactose-intolerant
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• Lactose tolerance appears to have evolved in northern European
cultures that relied upon dairy products.
• Ethnic groups in East Africa that rely upon dairy products are also
lactose tolerant but due to different mutations.
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Figure 3.28
Large biological
molecules
Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose
Disaccharides:
lactose, sucrose
Polysaccharides:
starch, cellulose
Dietary energy;
storage; plant
structure
Monosaccharide
Lipids
Long-term
energy storage
fats;
hormones
steroids
Fatty acid
Glycerol
Components of
a triglyceride
Amino
group
Proteins
Enzymes, structure,
storage, contraction,
transport, and others
Fats triglycerides;
Steroids
testosterone,
estrogen
Carboxyl
group
Side
group
Lactase
an enzyme,
hemoglobin
a transport protein
Amino acid
Phosphate
Base
Nucleic acids
Information
storage
DNA, RNA
Sugar
Nucleotide
Figure UN3-2
Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose
Disaccharides:
lactose, sucrose
Polysaccharides:
starch, cellulose
Dietary energy;
storage; plant
structure
Monosaccharide
Figure UN3-2a
Lipids
Functions
Long-term
energy storage
fats;
hormones
steroids
Components
Fatty acid
Glycerol
Components of
a triglyceride
Examples
Fats triglycerides;
Steroids
testosterone,
estrogen
Figure UN3-2b
Proteins
Functions
Components
Amino
group
Enzymes, structure,
storage, contraction,
transport, and others
Examples
Carboxyl
group
Side
group
Lactase
an enzyme,
hemoglobin
a transport protein
Amino acid
Figure UN3-2c
Nucleic acids
Functions
Components
Examples
Phosphate
Base
Information
storage
DNA, RNA
Sugar
Nucleotide
Figure UN3-2d
Primary structure
sequence of
amino acids
Secondary structure
localized folding
Tertiary structure
overall shape
Quaternary structure
found in proteins with
multiple polypeptides
Figure UN3-3
Base
Phosphate
group
Sugar
DNA
double helix
DNA strand
DNA nucleotide
Figure UN3-4